The present invention relates to a magnetoresistive effect composite head and a method of manufacturing the same and, more particularly, to a magnetoresistive effect composite head having a reproducing head portion and a magnetic recording head portion that exploits the magnetoresistive effect and a method of manufacturing the same.
In recent years, as the magnetic recording medium is becoming down-sized and its capacity is becoming large, the relative velocity between the magnetic read head and the magnetic recording medium is becoming small, and therefore an expectation for a magnetoresistive effect head (to be referred to as an MR head hereinafter) whose reproducing output does not depend on tape velocity has become increased. This MR head is described in "A Magnetoresistive Readout Transducer", IEEE TRANSACTION ON MAGNETICS, VOL. MAG--7, NO. 1, March 1971.
A GMR head which uses the giant magnetoresistive effect (to be referred to as GMR hereinafter) that can realize a further larger increase in output than that from the MR head has come to the forefront of the technology. This GMR head is expected as a next-generation MR head since the magnetoresistive effect in which a change in resistance corresponds to the cosine between the directions of magnetization of two adjacent magnetic layers (generally called "the spin-valve effect") causes a large change in resistance with a small operating field.
An MR head which uses this spin-valve effect is described in "Design, Fabrication & Testing of Spin-Valve Read Heads for High Density Recording", IEEE TRANSACTION ON MAGNETICS, VOL. 30, NO. 6, November 1994.
Referring to FIG. 6, reference numerals 51 and 52 denote two magnetic layers at a central region 116 in an ideal state that causes the spin-valve effect. By the exchange coupling that is obtained upon stacking an antiferromagnetic film 53 on this magnetic layer 51, the magnetic layer 51 turns itself into a magnetic pinned layer 51 in which its direction of magnetization is substantially aligned with the direction of the medium field which enters the head sensor portion. The other magnetic layer 52 which is adjacent to the magnetic pinned layer 51 via a conductive layer, e.g., a Cu layer, serves as a magnetic free layer 52 whose direction of magnetization is free to change in response to the medium field. Reference numerals 52A and 52B denote permanent magnets whose directions of magnetization are constant; 12 and 18, magnetic shields; and P1 and P2, magnetic poles. This stacked structure that produces the spin-valve effect is used as the major portion of a conventional magnetoresistive effect composite head shown in FIG. 7.
The conventional magnetoresistive effect composite head (to be abbreviated as the composite head hereinafter) shown in FIG. 7 will be described. The composite head shown in FIG. 7 has a slider main body 111 made of a ceramic material, and a pair of magnetic shields 112 and 118 stacked on the slider main body 111 and opposing each other through a predetermined gap. Stacked magnetic spacer layers 113 and 117 made of insulators are formed between the magnetic shields 112 and 118. A central region 116 and end regions 114 and 115 are formed in the magnetic spacer layers 113 and 117. The central region 116 is a stacked structure which produces the spin-valve effect. The end regions 114 and 115 are located on the two sides of and on the same plane as that of the central region 116 to supply a current and a bias field to the central region 116.
Reference numeral 120 denotes a protection film made of alumina or the like. A magnetoresistive effect element 110 formed of the central region 116 and end regions 114 and 115 constitutes a reproducing head that reads.
Of the magnetic shields 112 and 118, the upper shield 118 forms one magnetic pole P1. The other magnetic pole P2 is stacked, on a surface of the magnetic pole P1 which is opposite to the central region 116, via a magnetic gap 119 to lie parallel to the magnetic pole P1 (upper shield 118).
A coil (not shown) sandwiched by insulators is arranged slightly behind the magnetic poles P1 and P2. A magnetic flux leaking from the magnetic gap 119 between the magnetic poles P1 and P2 that are magnetized by the magnetic field generated by this coil performs recording. A structure in which this recording head and the reproducing head described above are stacked constitutes a practical magnetoresistive effect composite head that makes use of the spin-valve effect.
In this case, as shown in FIG. 6 that indicates the ideal state, the direction of magnetization of one of the two adjacent magnetic layers must be locked to be parallel to the medium field so that this magnetic layer becomes a magnetic pinned layer 51, and the other magnetic layer becomes a magnetic free layer 52 the magnetization of which is free to rotate in response to the medium field. This is indispensable in realizing appropriate head operation.
The direction of magnetization of this magnetic pinned layer is perpendicular to the easy axis of magnetization of the magnetic shields (upper and lower shields) constituting the composite head and of the magnetic poles of the inductive head (ID head) that records. When a heat magnetic field treatment is performed to stabilize the magnetization of the spin-valve magnetic pinned layer at the central region, the magnetic anisotropy of the magnetic shields and of the respective recording magnetic poles is reversed. In contrast, when a heat magnetic field treatment is performed to stabilize the magnetic anisotropy of the magnetic shields and of the recording magnetic poles, the magnetization of the spin-valve magnetic pinned layer becomes unstable. These problems present a large obstacle to putting a composite head made of a spin-valve element into practical use.